The present invention relates generally to apparatus and method for vacuum hot pressing of materials, particularly metals, under high temperatures in a vacuum or inert gas environment within a permanent type enclosure or chamber and subjecting the materials to an evenly distributed pressure provided over a relatively large work area with respect to the chamber interior.
As the need for lighter and/or stronger materials has advanced, particularly in such areas as aerospace constructions, interest has heightened in the technology of metal pressing, compacting and joining materials for the fabrication of parts and in metal treating such as, for example, diffusion bonding, powder metallurgy, vacuum brazing and thermo-mechanical processing of materials. Prior to the present invention several methods with attendant apparatus had been evolved for these purposes. There are, though, numerous and inherent disadvantages in the prior systems often leading to expensive and deleterious results. Thus, in the cases of certain materials it is desirable to work or subject them to pressing force with high values of force per unit area uniformly applied to the work or materials acted on over a relatively substantial work area and under high vacuum or inert gas environment at elevated temperatures. However, prior known equipment for properly doing so over any substantial or practically useful work area has been unduly expensive, sometimes requiring complicated methods, plural furnace chambers, or non-reusable or non-permanent type equipment components. Also, such prior equipment often has been of undesirably large or bulky construction or has a utilizable enclosed work area disproportionately small to the size of the enclosure or the associated press apparatus. In consequence, the capital expense has sometimes been so large as to impede growth in these technologies.
One attempt to overcome these drawbacks utilizes a vacuum furnance chamber having its wall penetrated by a small diameter ram (compared to the plan area of the work area acted upon) attached to a pressure distributing platen within the chamber and forming part of or acted on by the ram of an associated press apparatus in order to apply pressure to the workpiece within the chamber. Such construction requires that heavy and bulky backup supports to such internal movable platen be included within the vacuum chamber to provide distribution of the ram thrust over the platen and thus the work or workpiece area, since high heat within the furnace may otherwise distort the platen with resulting uneven pressure on the work so as to yield unsatisfactory results such as non-uniformly bonded materials. That construction, therefore, increases the size of the furnace chamber required to handle a given size or lot of workpieces or material. Available work space is also decreased and disproportionate costs incurred with respect to the size of the materials worked on. Moreover, there are self-evident difficulties of sealing the chamber wall against vacuum loss or gas leakage where it is penetrated by the ram.
Another method utilizes vacuum retort apparatus in the form of an envelope or chamber welded from thin metal sheet to hermetically contain the workpiece and is evacuated, sealed, heated externally, for example, by placing the envelope within a larger furnace, after which the heated retort is transferred to a press apparatus. There the workpiece is pressed upon by permanently deforming the retort which is then necessarily destroyed to gain access to the materials within. Obviously, such sheet metal retort technique suffers from the short life of the retort due to its single use, the further requirement of complete inspection of welds therein to insure vacuum tightness and a complexity of tooling required to align the enclosed work or workpieces with the pressure exerting portions of the press.
The present invention very largely overcomes the difficulties of such prior art methods and apparatus.